Flame-retardant thermosetting resin composition

Abstract: A flame-retardant thermosetting resin composition comprising a thermosetting resin and from 4 to 50% by weight, based on the composition, of (1) melamine-coated ammonium polyphosphate particles and/or (2) water-insoluble ammonium polyphosphate particles obtained by crosslinking the surface of melamine-coated ammonium polyphosphate particles with a compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group in the melamine molecule. Water-insoluble ammonium polyphosphate particles comprising melamine-coated ammonium polyphosphate particles with the surface thereof being crosslinked by a reaction between the melamine of the melamine-coated ammonium polyphosphate particles and a crosslinking agent having a functional group capable of reacting with the active hydrogen atoms belonging to the amino group in the melamine molecule. A process for producing water-insoluble ammonium polyphosphate particles comprising adhering or impregnating a crosslinking agent having a functional group capable of reacting with the active hydrogen atoms belonging to the amino group in the melamine molecule to or into the surface of melamine-coated ammonium polyphosphate particles and allowing the melamine of the melamine coat and the crosslinking agent to react.

Description: FIELD OF THE INVENTION This invention relates to a flame-retardant thermosetting resin composition containing a non-halogen type flame-retardant. More particularly, it relates to a flame-retardant thermosetting resin composition having high water resistance and excellent mechanical properties which contains, as a non-halogen type flame-retardant, (1) melamine-coated ammonium polyphosphate particles and/or (2) water-insoluble ammonium polyphosphate particles. BACKGROUND OF THE INVENTION Thermosetting resins such as epoxy resins, urethane resins and phenolic resins possess excellent heat resistance and mechanical strength and have therefore been used extensively, for example, as a molding material for electric and electronic parts, constructional materials and automobile parts, a coating, an adhesive, and an impregnating resin for impregnated paper. Flame retardation of these thermosetting resins has been achieved generally by addition of a halogen-containing organic compound or by halogenating part of the polymer chain. However, halogen-containing thermosetting resin compositions generate a corrosive halogenous gas on combustion, which has given rise to a problem. Ammonium polyphosphate has been proposed as a halogen-free flame-retardant, but it is very susceptible to hydrolysis because of its chemical structure so that molded articles obtained from a resin composition containing ammonium polyphosphate suffer from eluation or bleeding of the ammonium polyphosphate under a high temperature and high humidity condition. It has also been pointed out that compounding of such an inorganic compound as ammonium polyphosphate leads to reduction of mechanical properties of the resin composition. It has therefore been demanded to develop a flame-retardant thermosetting resin composition containing a flame-retardant which produces no halogenous gas on combustion, is not eluted, does not bleed out, and causes little reduction in mechanical characteristics of the resin. In order to meet the demand, a resin composition containing a metal hydrate as an inorganic flame-retardant has been proposed as disclosed in JP-A-3-190965 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), in which the metal hydrate undergoes an endothermic decomposition and dehydration reaction at the combustion temperature of the resin composition thereby suppressing combustion of the resin composition. However, since the flame retarding effect of the metal hydrate is very weak, desired flame retardation cannot be achieved unless it is used in a large quantity, and addition of a large quantity of the metal hydrate results in reduction in moldability of the resin composition and reduction in mechanical strength of molded articles of the resin composition. JP-A-4-227923 discloses an epoxy resin composition which is flame retarded with a carbon-forming non-halogen type flame-retardant containing ammonium polyphosphate, but the ammonium polyphosphate used is conventional one which is highly water-soluble and easily hydrolyzable. On the other hand, JP-A-1-108261 discloses a flame-retardant polymer composition containing synthetic resin-coated ammonium polyphosphate particles, and JP-A-5-9376 describes a flame-retardant urethane resin composition containing ammonium polyphosphate particles which are encapsulated by a melamine-formaldehyde resin or an epoxy resin. In these techniques, since the ammonium polyphosphate particles are coated or encapsulated with a synthetic resin, it seems that ammonium polyphosphate is prevented from being eluted and thereby from bleeding, but the publications has no mention of it. Further, the synthetic resin coat covering the individual ammonium polyphosphate particles is a cured resin and is no more reactive. Therefore, when added to a thermosetting resin, such a synthetic resin coat has poor compatibility with the thermosetting resin so that the resulting flame-retardant resin composition only provides molded articles having reduced mechanical strength. With respect to improvement on hydrolysis stability of ammonium polyphosphate, JP-B-53-15478 (the term "JP-B" as used herein means an "examined published Japanese patent application") discloses a process for obtaining modified ammonium polyphosphate comprising condensing ammonium phosphate and urea or crystalline urea phosphate under heating in the presence of 5 to 50% by weight, in terms of melamine, of melamine or melamine phosphate. However, the modified ammonium polyphosphate obtained by the process disclosed still has insufficient stability against hydrolysis for use as a component of a flame retardant for thermoplastic resins, thermosetting resins, coatings, flame-retardant paper, etc. JP-B-52-39930 discloses a process for obtaining melamine-added ammonium polyphosphate powder comprising uniformly mixing 100 parts by weight of ammonium polyphosphate and 60 parts by weight of melamine, heating the mixture at 320°C, cooling the heated product, and grinding the resulting fused product. However, because a product having been once fused is ground to powder, the resulting ammonium polyphosphate particles are not uniformly coated with melamine and are therefore still insufficient in hydrolysis stability. JP-A-61-103962 proposes a process for producing a finely divided and flowable flame-retardant mainly comprising powdered ammonium polyphosphate having hydrolysis stability, which process comprises preparing a suspension from ammonium polyphosphate, water, an organic suspending agent, and a melamine formaldehyde resin, heating the suspension at a temperature of 50 to 180°C under standard pressure or under pressure, and leaving the suspension to stand for 15 to 240 minutes to allow the resin component to harden. However, not only does the finely divided flame-retardant obtained have insufficient hydrolysis stability, but the particles undergo agglomeration during hardening of the resin component in the suspension, resulting in an increase of particle size. Therefore, no matter how fine the starting ammonium polyphosphate particles are, the initial particle size of the ammonium polyphosphate can hardly be maintained in the resulting flame-retardant. Such a finely divided flame-retardant, when added to thermoplastic resins, thermosetting resins, coatings or paper, causes reduction in mechanical strength of the final products. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thermosetting resin composition which exhibits excellent flame retardancy as well as heat resistance and mechanical strength without suffering from eluation or bleeding of a flame-retardant compounded therein and is therefore suitable as a molding material for electric and electronic parts, constructional materials and automobile parts, a coating, an adhesive, and an impregnating resin for impregnated paper. The present inventors have conducted extensive investigations to obtain a flame-retardant thermosetting resin composition containing a flame-retardant which produces no halogenous gas on combustion, is not eluted, does not bleed out, and causes little reduction in mechanical properties of the resin composition. As a result, they have found that a flame-retardant thermosetting resin composition meeting the above object is obtained by using, in place of the conventional ammonium polyphosphate particles, (1) melamine-coated ammonium polyphosphate particles in which melamine is chemically bonded onto the surface of ammonium polyphosphate particles by sublimation and/or (2) water-insoluble ammonium polyphosphate particles obtained by crosslinking the surface of the above-mentioned melamine-coated ammonium polyphosphate particles with a compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group in the melamine molecule present in the melamine of the melamine-coated ammonium polyphosphate particles, which compound may be called "a crosslinking agent". The present invention has been completed based on this finding. The present invention provides a flame-retardant thermosetting resin composition comprising a thermosetting resin and from 4 to 50% by weight, based on the composition, of either one or both of: (1) melamine-coated ammonium polyphosphate particles in which melamine is chemically bonded to the proton of the oxygen-proton bond originated from the release of ammonia from ammonium polyphosphate and whose melamine content is 0.5 to 20% by weight based on ammonium polyphosphate particles, and (2) water-insoluble ammonium polyphosphate particles obtainable by crosslinking the surface of melamine-coated ammonium polyphosphate particles (1) with 0.5-6 equivalents, based on the number of its functional groups per the amino group of melamine molecules of the melamine coat of the particles (1), of a compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group in the melamine molecule, the particles (1) and/or (2) having an average particle size of not greater than 15 µm. The flame-retardant thermosetting resin composition according to the present invention includes the following embodiments (1) to (5): 1) The thermosetting resin contains a glycidyl group, an isocyanate group, a methylol group or an aldehyde group. 2) The melamine-coated ammonium polyphosphate particles are those obtained by sublimating melamine so that it becomes chemically bonded to the surface of the ammonium polyphosphate particles. 3) The compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group of the melamine residues has an isocyanate group, a glycidyl group, a carboxyl group, a methylol group or an aldehyde group. 4) The compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group of the melamine residues has two or more functional groups. 5) The thermosetting resin is an epoxy resin, a rigid urethane resin, a soft urethane resin, a phenolic resin, a melamine resin, a guanamine resin, a xylene resin or a urea resin. DETAILED DESCRIPTION OF THE INVENTION The melamine-coated ammonium polyphosphate particles which can be used in the present invention comprise particles of ammonium polyphosphate represented by formula (I): wherein n is an integer of 2 or greater, the particles being coated with melamine. The melamine-coated ammonium polyphosphate particles can be obtained by, for example, the following method. In the first stage, particles of ammonium polyphosphate of formula (I) are put in a preheated heating and kneading apparatus, such as a kneader, and heated at such a temperature that they easily release the ammonia content thereof without being melted, i.e., at 300°C or lower, preferably from 200 to 300°C, for 0.5 to 5 hours. Thus, part of ammonia originally present in the ammonium polyphosphate in a stoichiometric amount is released (i.e., 5 to 10% by weight based on the stoichiometric amount of ammonia is released) to provide ammonium polyphosphate particles from which part of the ammonia content has been removed, whose 1% by weight aqueous suspension has a pH of 4.0 to 6.0, or ammonium polyphosphate particles in which the combined ammonia content is smaller than the stoichiometric amount in a known process for ammonium polyphosphate production (as disclosed in U.S. Patents 4,396,586 and 5,213,783). These ammonium polyphosphate particles will hereinafter referred to as ammonia-deficient ammonium polyphosphate particles. In the second stage, the ammonia-deficient ammonium polyphosphate particles are heated in the same apparatus at such a temperature that they are not melted and that melamine is capable of sublimation, i.e., at 350°C or lower, preferably from 250 to 300°C, at which temperature melamine is added thereto. Thus, melamine is sublimed and is added and/or adhered to the surface of the ammonia-deficient ammonium polyphosphate particles. In this context, the term "added" as used herein means that melamine is chemically bonded to the proton of the oxygen-proton bond originated from the release of ammonia from ammonium polyphosphate. The "added" melamine is thermally stable and is never released again by heating. The term "adhered" as used herein means that melamine is adsorbed on the surface of ammonium polyphosphate particles. On continuation of heating, the melamine adsorbed on the surface of the particles alternates sublimation and adsorption repeatedly and is meanwhile chemically bonded to the proton of the oxygen-proton bond. The proportion of the melamine to be charged is from 0.5 to 20% by weight, preferably from 2 to 15% by weight, more preferably 2 to 10% by weight, based on the ammonium polyphosphate particles. All the melamine charged is added and/or adhered onto the surface of the ammonium polyphosphate particles to obtain melamine-coated ammonium polyphosphate particles according to the present invention. Commercially available grades of ammonium polyphosphate may be utilized as starting ammonium polyphosphate particles. Examples of suitable grades include SUMISAFE-P (produced by Sumitomo Chemical Co., Ltd.), EXOLIT-422 or 700 (both produced by Hoechst AG), and PHOS-CHECK P/40 (produced by Monsanto Co., Ltd.). Ammonium polyphosphate (crystal form II) fine particles, as described in JP-A-4-300204 (corresponding to U.S. Patent 5,213,783), are also useful. The ammonium polyphosphate (crystal form II) fine particles can be obtained, for example, as follows. Equimolar amounts of diammonium hydrogenphosphate and phosphorus pentoxide (P 2 O 5 ) are mixed together, and the mixture is heated to a temperature of 290 to 300°C with stirring. A 77% by weight urea solution containing urea in an amount 0.5 times the molar quantity of the diammonium hydrogenphosphate is then added thereto by spraying, and the mixture is subsequently heated in an ammonia atmosphere at 250 to 270°C for several hours. The melamine to be used in the present invention may be any of commercial products available as a melamine monomer. The water-insoluble ammonium polyphosphate particles (hereinafter sometimes referred to simply as particles (2)) which can be used in the present invention comprise the above-mentioned melamine-coated ammonium polyphosphate particles (hereinafter sometimes referred to simply as particles (1)) with the melamine molecules in the melamine coat thereof being crosslinked with a compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group in the melamine molecules (hereinafter simply referred to as a functional group-containing compound). The particles (2) having such a structure are prepared, for example, by mixing the particles (1) and a functional group-containing compound, such as a formaldehyde aqueous solution, in a reactor equipped with a heating means and a stirring means or a kneading means, and heating the mixture to a temperature at which a crosslinking reaction among active hydrogen atoms easily takes place, i.e., at 80 to 200°C, preferably 100 to 150°C, for 0.5 to 2 hours. In the above-mentioned method, since monomolecules are used as the functional group-containing compound, the crosslinking reaction preferentially takes place on the individual melamine-coated ammonium polyphosphate particles without occurring agglomeration of the particles through the functional group-containing compound. The crosslinking reaction may be effected either with or without a solvent. Water, organic solvents or mixtures of two or more thereof may be used as a solvent. The functional group-containing compound is used in an amount of from 0.5 to 6 equivalents, preferably 1 to 2 equivalents, in terms of the functional groups per the amino group of melamine molecules of the melamine coat of the particles (1). If the proportion of the functional group is less than 0.5 equivalent, the crosslinking among melamine molecules is not sufficient only to provide melamine-coated ammonium polyphosphate particles susceptible to hydrolysis. If the proportion of the functional group is larger than 6 equivalents, the excess remains unreacted in the reaction mixture. The functional groups capable of reacting with active hydrogen atoms belonging to the amino group in melamine molecule include an isocyanate group, an hydroxymethyl group, a formyl group, and an epoxy group. Examples of compounds containing one or more functional groups include those having an isocyanate group(s), such as 1,6-hexane diisocyanate, 1,1'-methylenebis(4-phenyl isocyanate), 3,3,-dimethyldiphenyl-4,4'-diisocyanate, and naphthylene-1,5-diisocyanate; those having a methylol group, such as methylol urea, methylol melamine, trimethylolethane, and trimethylolpropane; those having an aldehyde group, such as formaldehyde, malonaldehyde, and glyoxal; those having an epoxy group, such as ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, and various epoxy resins, e.g., bisphenol A type epoxy resins, phenol novolak epoxy resins, and cyclic aliphatic epoxy resins. All the available commercial products may be utilized. When the water-insoluble polyphosphate particles are added to the thermosetting resin, the functional groups capable of reacting with active hydrogen atoms belonging to the amino group in melamine molecule include an isocyanate group, a glycidyl group, a carboxyl group, a methylol group, and an aldehyde group. The functional group-containing compound may have one or more than one functional groups. Specific examples of the functional group-containing compound include those having an isocyanate group, such as hexamethylene diisocyanate and toluylene diisocyanate; those having a glycidyl group, such as various epoxy resins, e.g., bisphenol A and phenol novolak; those having a carboxyl group, such as oxalic acid, malonic acid and phthalic acid; those having a methylol group, such as trimethylolpropane and trimethylolethane; and those having an aldehyde group, such as formaldehyde, glyoxal, and malonaldehyde. The melamine-coated ammonium polyphosphate particles (1) and/or water-insoluble ammonium polyphosphate particles (2) are used in an amount of from 4 to 50% by weight, preferably from 10 to 45% by weight, based on the thermosetting resin composition. If the amount of these flame-retardant is less than 3% by weight, sufficient flame retardancy cannot be obtained. If it exceeds 60% by weight, the resin composition suffers from considerable reductions in mechanical properties for the improvement in flame retardancy, failing to withstand practical use. Suitable thermosetting resins which can be applied to the present invention include those having a glycidyl group, an isocyanate group, a methylol group or an aldehyde group. Preferred of them are epoxy resins, rigid urethane resins, soft urethane resins, phenolic resins, melamine resins, guanamine resins, xylene resins, and urea resins. Additionally, unsaturated polyester resins and diallyl phthalate resins are also suitable as thermosetting resins. There are active hydrogen atoms belonging to the amino group of melamine molecules on the surface of the melamine-coated ammonium polyphosphate particles (1). In the water-insoluble ammonium polyphosphate particles (2), the active hydrogen atoms in the melamine molecules in the melamine coat of the particles (1) have been reacted with the functional group-containing compound to form a crosslinked structure among melamine molecules on the individual particles. The active hydrogen atom in the melamine molecules remains in the melamine coat of particles (2) as far as the degree of crosslinking among melamine molecules is moderately controlled. At the stage where the above-mentioned preferred thermosetting resin is cured, the residual active hydrogen atom of the particles (1) or (2) is reacted with such a functional group as a glycidyl group, an isocyanate group, a methylol group or an aldehyde group of the thermosetting resin to form a chemical bond between the particles (1) or (2) and the thermosetting resin. As a result, the particles (1) or (2) and the thermosetting resin exhibit markedly improved compatibility with each other, and addition of these particles brings about no serious reductions in mechanical properties. If desired, the thermosetting resin composition according to the present invention may further contain other additives commonly employed for general thermosetting resins, such as curing agents, curing accelerators, other known flame-retardants, flame-retardant promoters, colorants, surface active agents, heat stabilizers, plasticizers, photostabilizers, solvents, and the like. The present invention will now be illustrated in greater detail with reference to Examples, but it should be understood that the present invention is not construed as being limited thereto. All the percents, parts, and ratios are given by weight unless otherwise indicated. Samples prepared in Examples and Comparative Examples were evaluated in accordance with the following test methods. 1) Flame Retardancy: Tested according to the vertical combustion test specified in "Combustion Test of Plastic Materials for Appliance Parts" in UL Subject 94 (Underwriters Laboratories Inc.). Test piece thickness: 1.6 mm (1/16 inch). 2) Oxygen Index (O.I.): Determined in accordance with JIS K7201 (Combustion Test Method for High Polymeric Materials by Oxygen Index Method). 3) Hot-Water Immersion Test: A 100 mm long, 100 mm wide and 2 mm thick test piece was prepared by hot press molding, and the surface resistivity of the test piece was measured with a vibrating reed electrometer, manufactured by Takeda Riken Industry Co., Ltd. The test piece was immersed in hot water at 95°C for 2 hours and taken out. The water on the test piece was wiped off with a wiping paper, and the surface resistivity was measured again. Samples which underwent a considerable reduction in surface resistivity due to the immersion in hot water were regarded as poor in bleed resistance. 4) Tensile Strength and Tensile Elongation: Measured in accordance with JIS K7113 (Tensile Test Method for Plastics) using test pieces of 100 mm length, 20 mm width and 2 mm thickness. 5) Flexural Strength: Measured in accordance with JIS K7203 (Bending Test Method for Rigid Plastics) using test pieces of 100 mm length, 25 mm width and 2 mm thickness. The melamine-coated ammonium polyphosphate particles used in the following Examples were prepared by treating ammonium polyphosphate (crystal form II) fine particles as follows. In a kneader previously heated to 280°C was charged 2000 g of ammonium polyphosphate (crystal form II) fine particles having an average particle size of 6.4 µm and heated with stirring for 3 hours in a nitrogen or inert gas atmosphere to release ammonia. To the resulting ammonia-deficient ammonium polyphosphate fine particles was added 200 g of melamine, and the mixture was heated and mixed at 280°C for 4 hours with the top of the kneader closed while maintaining the form of the ammonium polyphosphate particles. Thus, 2100 g of melamine-coated ammonium polyphosphate particles were obtained. Observation under an electron microscope revealed that the surface of the individual ammonium polyphosphate (crystal form II) fine particles is uniformly coated with melamine. The ammonium polyphosphate (crystal form II) fine particles mentioned above were obtained by the following method. In a 5 ℓ table kneader preheated to 290 to 300°C were charged 660 g (5 mol) of diammonium hydrogenphosphate and 710 g (5 mol) of phosphorus pentoxide, and the mixture was heated with stirring in a nitrogen atmosphere. After 20 minutes, 195 g of a 76.9% urea solution heated to 80°C was added thereto by spraying. Subsequently, the mixture was heated at 250 to 270°C for 2.5 hours in an ammonia atmosphere to obtain 160 g of ammonium polyphosphate fine particles. Since the resulting fine particles was a mixture of primary particles and a small proportion of agglomerates, it was ground in a grinder AP-B Model, manufactured by Hosokawa Micron Corp., in an ammonia atmosphere so as to separate the agglomerates into primary particles. X-Ray diffractometry revealed that the resulting ammonium polyphosphate fine particles were of the crystal form II and had an average particle size of 6.4 µm. EXAMPLE 1 A mixture of 71.2 parts of a bisphenol A type epoxy resin EPIKOTE 828, produced by Yuka Shell Epoxy Co., Ltd., and 20 parts of melamine-coated ammonium polyphosphate was thoroughly dispersed, and 8.8 parts of diethylenetriamine was added thereto as a curing agent, followed by thoroughly mixing. After degassing, the mixture was heated at 30°C for 60 minutes and hot press molded at 100°C for 15 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample a) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 1. EXAMPLE 2 Test pieces (hereinafter designated sample b) were prepared and tested in the same manner as in Example 1, except for using a resin composition consisting of 53.4 parts of EPIKOTE 828, 40 parts of melamine-coated ammonium polyphosphate particles, and 6.6 parts of diethylenetriamine. The results of the tests are shown in Table 1. EXAMPLE 3 A mixture of 51 parts of a polyisocyanate compound DN-980S, produced by Dainippon Ink & Chemicals, Inc., 49 parts of a polyester polyol D-220, produced by Dainippon Ink & Chemicals, Inc., and 13 parts of melamine-coated ammonium polyphosphate was thoroughly mixed. After degassing, the mixture was hot press molded at 150°C for 30 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample c) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, and a tensile test. The results obtained are shown in Table 2. EXAMPLE 4 Test pieces (hereinafter designated sample d) were prepared and tested in the same manner as in Example 3, except for changing the amount of the melamine-coated ammonium polyphosphate particles to 20 parts. The results of the tests are shown in Table 2. EXAMPLE 5 A mixture of 87 parts of a molding melamine resin (containing cellulose powder), produced by Fuji Kasei K.K., and 13 parts of melamine-coated ammonium polyphosphate particles was hot press molded at 165°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample e) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 3. EXAMPLE 6 A mixture of 87 parts of a molding phenolic resin (containing cellulose powder), produced by Fudo K.K., and 13 parts of melamine-coated ammonium polyphosphate particles was hot press molded at 170°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample f) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 3. EXAMPLE 7 A mixture of 94 parts of a molding phenolic resin (containing cellulose powder), produced by Fudo K.K., and 6 parts of melamine-coated ammonium polyphosphate particles was hot press molded at 170°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample g) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 3. COMPARATIVE EXAMPLE 1 89 parts of a bisphenol A type epoxy resin EPIKOTE 828 and 11 parts of diethylenetriamine as a curing agent were mixed and degassed. The mixture was heated at 30°C for 60 minutes and then hot press molded at 100°C for 15 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample h) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 1. COMPARATIVE EXAMPLE 2 Test pieces (hereinafter designated sample i) were prepared and tested in the same manner as in Example 1, except for replacing the melamine-coated ammonium polyphosphate particles with 20 parts of ammonium polyphosphate SUMISAFE-P, produced by Sumitomo Chemical Co., Ltd. The results of the tests are shown in Table 1. COMPARATIVE EXAMPLE 3 Test pieces (hereinafter designated sample j) were prepared and tested in the same manner as in Example 1, except for replacing the melamine-coated ammonium polyphosphate particles with 20 parts of ammonium polyphosphate (crystal form II) fine particles. The results of the tests are shown in Table 1. COMPARATIVE EXAMPLE 4 Test pieces (hereinafter designated sample k) were prepared and tested in the same manner as in Example 1, except for replacing the melamine-coated ammonium polyphosphate particles with 20 parts of ammonium polyphosphate EXOLIT-462, produced by Hoechst AG. The results of the tests are shown in Table 1. COMPARATIVE EXAMPLE 5 Test pieces (hereinafter designated sample 1) were prepared and tested in the same manner as in Example 1, except for replacing the melamine-coated ammonium polyphosphate particles with 80 parts of magnesium hydroxide KISUMA 5A, produced by Kyowa Kagaku Kogyo K.K. The results of the tests are shown in Table 1. COMPARATIVE EXAMPLE 6 51 parts of polyisocyanate DN-980S and 49 parts of polyester polyol D-220 were mixed and degassed. The mixture was hot press molded at 150°C for 30 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample m) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, and a tensile test. The results obtained are shown in Table 2. COMPARATIVE EXAMPLE 7 Test pieces (hereinafter designated sample n) were prepared and tested in the same manner as in Example 3, except for replacing the melamine-coated ammonium polyphosphate particles with 20 parts of ammonium polyphosphate SUMISAFE-P. The results of the tests are shown in Table 2. COMPARATIVE EXAMPLE 8 Test pieces (hereinafter designated sample p) were prepared and tested in the same manner as in Example 3, except for replacing the melamine-coated ammonium polyphosphate particles with 20 parts of ammonium polyphosphate (crystal form II) fine particles. The results of the tests are shown in Table 2. COMPARATIVE EXAMPLE 9 Test pieces (hereinafter designated sample q) were prepared and tested in the same manner as in Example 3, except for replacing the melamine-coated ammonium polyphosphate particles with 100 parts of magnesium hydroxide KISUMA 5A. The results of the tests are shown in Table 2. COMPARATIVE EXAMPLE 10 A molding melamine resin (containing cellulose powder), produced by Fuji Kasei K.K., was hot press molded at 165°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample r) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 3. COMPARATIVE EXAMPLE 11 Test pieces (hereinafter designated sample s) were prepared and tested in the same manner as in Example 5, except for replacing the melamine-coated ammonium polyphosphate particles with 13 parts of ammonium polyphosphate SUMISAFE-P. The results of the tests are shown in Table 3. COMPARATIVE EXAMPLE 12 A molding phenolic resin (containing cellulose powder), produced by Fudo K.K., was hot press molded at 170°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample t) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 3. COMPARATIVE EXAMPLE 13 Test pieces (hereinafter designated sample u) were prepared and tested in the same manner as in Example 6, except for replacing the melamine-coated ammonium polyphosphate particles with 13 parts of ammonium polyphosphate SUMISAFE-P. The results of the tests are shown in Table 3. Containing no ammonium polyphosphate, the epoxy resin composition of Comparative Example 1 exhibits no flame retardancy. The epoxy resin compositions of Comparative Examples 2 and 3 containing ammonium polyphosphate particles (SUMISAFE-P) or ammonium polyphosphate (crystal form II) fine particles as a flame-retardant undergo a serious reduction in surface resistivity due to hot-water immersion and suffer from eluation or bleeding of the flame-retardant. The epoxy resin composition of Comparative Example 4 has deteriorated mechanical properties, although it is flame-retardant, undergoes no reduction in surface resistivity even when immersed in hot water, and has satisfactory bleed resistance. The epoxy resin composition of Comparative Example 5 contains magnesium hydroxide (KISUMA 5A) as a flame-retardant in a proportion as high as 50% but still fails to have flame retardancy. To the contrary, the epoxy resin compositions of Examples 1 and 2 containing melamine-coated ammonium polyphosphate particles exhibit high flame retardancy and satisfactory bleed resistance, while suppressing reduction in mechanical properties. The above considerations also apply to the thermosetting resin compositions of Examples 3 to 7 and Comparative Examples 6 to 13. REFERENCE EXAMPLE 1 Preparation of Water-insoluble Ammonium Polyphosphate Particles In a 5 ℓ kneader equipped with a heating and kneading means and a degassing means were charged 1000 g of melamine-coated ammonium polyphosphate particles and 120 g of 37% formalin, mixed at room temperature for 30 minutes, and further mixed at 100°C for an additional period of 1 hour to obtain 1005 g of insoluble ammonium polyphosphate particles in which about 50% of the active hydrogen atoms belonging to the amino group of the melamine present in the melamine coat of the melamine-coated ammonium polyphosphate particles was crosslinked with an aldehyde group. The resulting particles are designated water-insoluble ammonium polyphosphate particles (A). REFERENCE EXAMPLE 2 Preparation of Water-insoluble Ammonium Polyphosphate Particles In a 5 ℓ flask equipped with a heating and kneading means and a refluxing means were charged 1000 g of melamine-coated ammonium polyphosphate particles and 900 g of toluene. Then, 132 g of hexamethylene diisocyanate and 2.6 g of NIKKA OCTHIX "Sn" (metal content 28%) catalyst were added thereto, followed by mixing at room temperature. The temperature was elevated to the refluxing temperature, at which the mixture was further mixed for 2 hours. After cooling, the mixture was filtered and dried in a drier at 100°C for 1 hour to obtain 1080 g of insoluble ammonium polyphosphate particles in which about 50% of the active hydrogen atoms belonging to the amino group of the melamine present in the melamine coat of the melamine-coated ammonium polyphosphate particles was crosslinked with an isocyanate group. The resulting particles are designated water-insoluble ammonium polyphosphate particles (B). EXAMPLE 8 A mixture of 71.2 parts of a bisphenol A type epoxy resin EPIKOTE 828 and 20 parts of water-insoluble ammonium polyphosphate particles (A) obtained in Reference Example 1 was thoroughly mixed, and 8.8 parts of diethylenetriamine was added thereto as a curing agent, followed by thoroughly mixing. After degassing, the mixture was heated at 30°C for 60 minutes and hot press molded at 100°C for 15 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample A) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 4. EXAMPLE 9 Test pieces (hereinafter designated sample B) were prepared and tested in the same manner as in Example 8, except for using a resin composition consisting of 71.2 parts of EPIKOTE 828, 20 parts of water-insoluble ammonium polyphosphate particles (B) obtained in Reference Example 2, and 8.8 parts of diethylenetriamine. The results of the tests are shown in Table 4. EXAMPLE 10 A mixture of 51 parts of a polyisocyanate compound DN-980S, 49 parts of a polyester polyol D-220, and 13 parts of water-insoluble ammonium polyphosphate particles (A) obtained in Reference Example 1 was thoroughly dispersed. After degassing, the mixture was hot press molded at 150°C for 30 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample C) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, and a tensile test. The results obtained are shown in Table 5. EXAMPLE 11 Test pieces (hereinafter designated sample D) were prepared and tested in the same manner as in Example 10, except for changing the amount of the water-insoluble ammonium polyphosphate particles (A) to 20 parts. The results of the tests are shown in Table 5. EXAMPLE 12 A mixture of 87 parts of a molding melamine resin (containing cellulose powder), produced by Fuji Kasei K.K., and 13 parts of water-insoluble ammonium polyphosphate particles (A) obtained in Reference Example 1 was hot press molded at 165°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample E) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 6. EXAMPLE 13 A mixture of 90 parts of a molding phenolic resin (containing cellulose powder), produced by Fudo K.K., and 10 parts of water-insoluble ammonium polyphosphate particles (A) obtained in Reference Example 1 was hot press molded at 170°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample F) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 6. EXAMPLE 14 A mixture of 94 parts of a molding phenolic resin (containing cellulose powder), produced by Fudo K.K., and 6 parts of water-insoluble ammonium polyphosphate particles (B) obtained in Reference Example 2 was hot press molded at 170°C for 4 minutes to prepare a flat plate. Test pieces of prescribed sizes (hereinafter designated sample G) were cut out of the plate and subjected to a flame retardancy test, measurement of O.I., a hot-water immersion test, a tensile test, and a bending test. The results obtained are shown in Table 6. COMPARATIVE EXAMPLE 14 Test pieces (hereinafter designated sample I) were prepared and tested in the same manner as in Example 8, except for replacing the water-insoluble ammonium polyphosphate particles (A) with 20 parts of ammonium polyphosphate (crystal form II) fine particles. The results of the tests are shown in Table 4. COMPARATIVE EXAMPLE 15 Test pieces (hereinafter designated sample J) were prepared and tested in the same manner as in Example 8, except for replacing the insoluble ammonium polyphosphate particles (A) with 20 parts of ammonium polyphosphate EXOLIT-462. The results of the tests are shown in Table 4. COMPARATIVE EXAMPLE 16 Test pieces (hereinafter designated sample K) were prepared and tested in the same manner as in Example 8, except for replacing the insoluble ammonium polyphosphate particles (A) with 80 parts of magnesium hydroxide KISUMA 5A. The results of the tests are shown in Table 4. COMPARATIVE EXAMPLE 17 Test pieces (hereinafter designated sample M) were prepared and tested in the same manner as in Example 10, except for replacing the water-insoluble ammonium polyphosphate particles (A) with 20 parts of ammonium polyphosphate (crystal form II) fine particles. The results of the tests are shown in Table 5. COMPARATIVE EXAMPLE 18 Test pieces (hereinafter designated sample N) were prepared and tested in the same manner as in Example 10, except for replacing the water-insoluble ammonium polyphosphate particles (A) with 100 parts of magnesium hydroxide KISUMA 5A. The results of the tests are shown in Table 5. COMPARATIVE EXAMPLE 19 Test pieces (hereinafter designated sample Q) were prepared and tested in the same manner as in Example 12, except for replacing the water-insoluble ammonium polyphosphate particles (A) with 13 parts of ammonium polyphosphate SUMISAFE-P. The results of the tests are shown in Table 6. COMPARATIVE EXAMPLE 20 Test pieces (hereinafter designated sample S) were prepared and tested in the same manner as in Example 13, except for replacing the water-insoluble ammonium polyphosphate particles (A) with 10 parts of ammonium polyphosphate SUMISAFE-P. The results of the tests are shown in Table 6. Containing no ammonium polyphosphate, the epoxy resin composition of Comparative Example 1 exhibits no flame retardancy. The epoxy resin composition of Comparative Example 14 containing ammonium polyphosphate (crystal form II) fine particles as a flame-retardant undergoes a serious reduction in surface resistivity due to hot-water immersion and suffers from eluation or bleeding of the flame-retardant. The epoxy resin composition of Comparative Example 15 has deteriorated mechanical properties, although it is flame-retardant, undergoes no reduction in surface resistivity even when immersed in hot water, and has satisfactory bleed resistance. The epoxy resin composition of Comparative Example 16 contains magnesium hydroxide (KISUMA 5A) as a flame-retardant in a proportion as high as 50% but still fails to have flame retardancy. To the contrary, the epoxy resin compositions of Examples 8 and 9 containing water-insoluble ammonium polyphosphate particles exhibit high flame retardancy and satisfactory bleed resistance, while suppressing reductions in mechanical properties. The above considerations also apply to the thermosetting resin compositions of Examples 10 to 14 and Comparative Examples 17 to 20. As described and demonstrated above, the flame-retardant thermosetting resin compositions according to the present invention which contain (1) melamine-coated ammonium polyphosphate particles and/or (2) water-insoluble ammonium polyphosphate particles as a flame-retardant produce no halogenous gas, suffer from no eluation or no bleeding of the flame-retardant (1) and/or (2), and undergo little reduction in mechanical properties. Hence, the flame-retardant thermosetting resin compositions of the present invention are suitable for wide use as, for example, a molding material for electric and electronic parts, constructional materials and automobile parts, a coating, an adhesive, and an impregnating resin for impregnated paper.

Claims: A flame-retardant thermosetting resin composition comprising a thermosetting resin and from 4 to 50% by weight, based on the composition, of either one or both of: (1) melamine-coated ammonium polyphosphate particles in which melamine is chemically bonded to the proton of the oxygen-proton bond originated from the release of ammonia from ammonium polyphosphate and whose melamine content is 0.5 to 20% by weight based on ammonium polyphosphate particles, and (2) water-insoluble ammonium polyphosphate particles obtainable by crosslinking the surface of melamine-coated ammonium polyphosphate particles (1) with 0.5-6 equivalents, based on the number of its functional groups per the amino group of melamine molecules of the melamine coat of the particles (1), of a compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group in the melamine molecule, the particles (1) and/or (2) having an average particle size of not greater than 15 µm. A flame-retardant thermosetting resin composition according to Claim 1, wherein said thermosetting resin is a thermosetting resin containing a glycidyl group, an isocyanate group, a methylol group or an aldehyde group. A flame-retardant thermosetting resin composition according to Claim 1 or Claim 2, wherein said melamine-coated ammonium polyphosphate particles are obtainable by sublimating melamine so that it becomes chemically bonded to the surface of the ammonium polyphosphate particles. A flame-retardant thermosetting resin composition according to any preceding Claim, wherein said compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group of the melamine residues has an isocyanate group, a glycidyl group, a carboxyl group, a methylol group or an aldehyde group. A flame-retardant thermosetting resin composition according to any preceding Claim, wherein said compound having a functional group capable of reacting with active hydrogen atoms belonging to the amino group of the melamine residues has two or more functional groups. A flame-retardant thermosetting resin composition according to any preceding Claim, wherein said thermosetting resin is an epoxy resin, a rigid urethane resin, a soft urethane resin, a phenolic resin, a melamine resin, a guanamine resin, a xylene resin or an urea resin.

Inventors: FUKUMURA TIKASHI, INOUE KOUJI, IWATA MASUO, SEKI MIKA, TAKAHASHI RYOJI, TANAKA MASAYA, FUKUMURA, TIKASHI, INOUE, KOUJI, IWATA, MASUO, SEKI, MIKA, TAKAHASHI, RYOJI, TANAKA, MASAYA
Applicants: CHISSO CORP, CHISSO CORPORATION
Application year: 1994
Main classification: C08K9
IPC codes: C08K3, C08K9, C08K5